Field of the Invention
The present invention generally relates to apparatus and methods for supplying respiratory gas under positive pressure to a sleeping user, such as in the treatment of obstructive sleep apnea (OSA). More particularly, the present invention relates to such apparatus and methods in which a condition of a user's body is sensed. Even more particularly, the present invention relates to such apparatus and methods featuring a gas supply that is responsive to breathing and that includes a valve in the control mechanism.
Description of the Related Art
A common method of treating obstructive sleep apnea (OSA) involves a pressure device that provides breathing gases, typically air, to a user (often referred to as the patient) while the user is asleep. These machines fall into the broad classification of PAP (positive airway pressure) devices or CPAP (continuous PAP) devices.
Within this broad classification, there are wide variations. For example, some machines provide different pressure during user inspiration than during user expiration (Bi PAP), some machines provide an auto-setting or autotitrating mode, wherein the supplied pressure varies through the period of use in response to detected events. In this context, detected events may include snoring, hypopneas and obstructive breathing. Some machines respond to user awakening and mask removal, for example, by reducing the delivered pressure. Some machines deliver a predetermined set pressure, which may be delivered at the same pressure night after night or which may be varied night by night by physical adjustment or by automatic adjustment by the unit. Some machines include a ramp function that begins automatically or that begins by user selection. The ramp function causes the machine to commence operation at a low pressure, which is sometimes settable, and to gradually increase to a higher pressure, which may be a predetermined treatment pressure or which may be an intermediate pressure.
The machines typically provide controlled pressure delivery. For example, the machines typically include a flow generator, a pressure sensor that senses the pressure being delivered to the user, and a feedback control that controls the output of the flow generator based upon a sensor signal so that the sensed pressure is maintained close to a demand pressure. Alternatively, the flow generator may include a fan that generates a known pressure and flow response. The output of the flow generator can be controlled to deliver a desired pressure using feedback from a flow sensor in a circuit that is connected to the flow generator. Alternatively, the flow generator may include a fan that provides a substantially uniform pressure at a given rotation speed across a useful range of flow. Pressure then can be controlled by setting a constant motor speed.
Even for the lower pressure at the start of a ramp cycle, most of the machines supply a minimum pressure of 3 cmH2O or more. The minimum pressure is more comfortable for the user than the full treatment pressure and results in a sufficient flow of breathing gases through a supply line to the user so that breathing gases exit through a bias flow or a controlled leak port provided at or near a user interface that is connected to the supply line.